Endovascular radiation treatment is the todays method of choice to prevent formation of scar tissue in a blood vessel which has been injured in various ways, for example, as trauma from surgical or diagnostic procedures. One area of the vascular system of particular concerns with respect to such injury is coronary arteries that are subjected to procedures for removing or reducing blockages due to plaque within the arteries. Partial and even complete blockage of the coronary arteries by the formation of an arteriosclerotic plaque is well known and a serious medical problem. Such blockages may be treated using arterectomy devices which mechanically remove the plaque, hot or cold lasers which vaporize the plaque, stents which hold the artery open and other devices and procedures well known in the art. The most common of them is the percutaneous transluminal coronary angioplasty, more commonly referred to as balloon angioplasty.
In this procedure a catheter having an inflatable balloon at its distal end is introduced into the coronary artery, the uninflated balloon is positioned at a stenotic site and the balloon is inflated. Inflation of the balloon disrupts and flattens the plaque against the arterial wall and stretches the arterial wall, resulting in enlargement of the intraluminal passageway and increased bloodflow. After such extension, the balloon is deflated and the balloon catheter removed.
Long term success of balloon angioplasty procedures is largely limited due to restenosis or re-closing of the intraluminal passageway through the artery by formation of scar tissue. Restenosis is experienced in approximately 30 to 50% of the patients within six months after balloon angioplasty. Apparently restenosis is to a significant extend a natural healing response to the vessel injury caused by inflation of the angioplasty balloon.
Such injury of the vessel typically initiates the bodies own natural repair and healing process. During the healing process, fibrin and plathelets rapidly accumulate in the endothelium and vascular smooth muscle cells proliferate and migrate into the intima. The formation of scar tissue by smooth muscle proliferation (hyperplasia) is believed to be a major contributor to restenosis following balloon angioplasty of the coronary artery.
Prior attempts to inhibit restenosis have included the use of various light therapies, chemotherapeutical agents, stents, arterectomy devices, hot and cold lasers and so on. The most promising approach to inhibit restenosis is the use of endovascular radiation therapy, i.e. the exposure of the restenotic site to ionizing or radioactive radiation.
Although endovascular radiation therapy in general has been applied advantageously, the devices available for delivery of radiation sources and the radiation sources themselves have certain drawbacks which limit their usefulness. Typically, the devices include a catheter, which is directed by way of a guide wire inserted therein to the site of treatment. The catheter is then used to internally direct the radiation source to the site of treatment.
One typical problem encountered with the catheter and/or the radiation source is related to stiffness of the source which is mostly directly proportional to its length. Thus shorter radiation sources are typically used to allow them to follow the bends of the artery. To irradiate the entire site of the vessel to be treated a so-called “stepping-treatment” is then employed, wherein the radiation source is moved back and forth in the vessel. Since, however, exact positioning is not possible in a constantly moving vessel, irradiation is not precisely controllable in this “stepping-treatment”. Thus, long sources are desirable which allow for one-step treatment of the site in its entire length.
For example, U.S. Pat. No. 5,833,593 discloses a flexible source wire which is modified at its treatment end to receive a radioactive element. A plug seals the unmodified section of the source from the lumen of the modified segment or container which contains the radioactive element. Both ends of the source wire are sealed to prevent leakage of radioactivity. The source wire is then inserted in a catheter for guiding the same to the treatment site. The modified section or container itself is rigid and is only flexibly linked to the remainder, unmodified portion of the source.
From U.S. Pat. No. 5,683,345 an apparatus and a method are known which apparatus includes an elongated flexible catheter tube having proximal and distal end portions with one or more lumina extending therebetween. One or more treating elements or seeds containing radioactive material are positionable within the first lumen and are movable between the proximal and distal end portions under the force of liquid flowing through the lumina. The radiation source used according this document consists of individual treating elements which may be joined together to form a train of treating elements by use of several length of high tempered spring wire to prevent the treating elements from becoming too spaced apart while moving through the catheter.
Other typical drawbacks encountered with prior art radiation sources and devices for delivering the same to the site to be treated are related to the duration of exposure, controllability of the radiation exposure (dosage, homogeneity of treatment), the necessity to conduct a “stepping-treatment”, or difficulties in completely and controllably retracting the radiation source from the catheter and therefore the risk of undesirable exposure of both the patient and any medical personal handling the treatment device. It is the object of the invention to overcome these and other drawbacks of prior art radiation sources.